New player confused

Hey guysI was thinking of starting Wow since I have a lot of time on my hands and nothing better to play.Could someone explain the difference between classic wow and wrath of the lich king? Im guessing It's basically DLC but they have separate options in the launcher so I'm not sure which one to press.I also saw someone say "wait for new wotlk server until u start playing". Is this something to worry about or are the servers good enough as they are?From what I've seen wow players basically treat the different patches (like tbc and wotlk) like different games so is that something i need to research or can i just play it blindly?